1. Field of the Invention
The present invention relates to power factor correction for AC to DC power converters, and more specifically, to AC to DC power converters having power factor correction circuitry utilizing a minimal component count and minimal IC pin count without loss of performance.
2. Brief Description of the Related Art
In most AC to DC power converters, it is convenient to have the circuit act as a pure resistor to the AC input line voltage. To achieve this, active power factor correction (PFC) can be implemented which, for an AC input line voltage, produces an AC input line current.
It also is important to produce a sinusoidal input current which has a low total harmonic distortion (THD). THD and power factor (PF) represent performance measurements of how well the PFC circuit works. A power factor (PF) of 1.0 represents the highest achievable, and a THD lower than about 15% is acceptable in practice.
A typical solution for providing active power factor correction is shown in circuit 2 of FIG. 1. Circuit 2 has a boost-type converter topology and a PFC IC 4 such as the Motorola 34262. The resulting circuit requires a voltage divider network (resistors 6 and 8 and capacitor 10) for sensing the AC rectified line input. Additionally, a secondary winding on the boost inductor 12 detects the zero-crossing of the inductor current. Also, a current sensing resistor 14 in the source of the boost switch 16 shapes the peak inductor current and detects an over-current condition. A voltage-divider network (resistors 18 and 20) senses and regulates a constant DC bus voltage and detects an over-voltage condition due to load transients. A compensation capacitor 22 is required for a stable loop response.
Accordingly, the need exists in the prior art for implementation of a simpler active power factor correction (PFC) circuit having fewer components.